The present invention relates to a microporous material usable particularly in the ceramic industry, and of which the pore size is close to that of gypsum plaster.
One of the applications of the invention of this material is the manufacture of moulds for the sanitary industry. The ceramic articles of the sanitary industry are obtained by pouring a clayey barbotine into a plaster mould. The porous nature of the plaster permits the percolation of the water of the barbotine, casting slip or slurry, and the hardening or setting of the moulded material, which takes the name "green body" and is solid and can be removed from the mould, then despatched to installations for drying, firing, and glazing.
It is required of the mould to have:
(a) a good surface condition, indispensable because it conditions the exterior aspect of the finished product and the obtainment of a homogeneous glaze; PA1 (b) sufficient mechanical strength to permit handling without too much risk of deterioration, it is acknowledged that a tensile strength of 50 bars is sufficient; PA1 (c) a porosity and a pore size adapted to permit, for example, the obtainment of a "green body" 10 mm in thickness after a water percolation time of 1-2 hours.
In practice a very fine plaster is used, mixed with water under vacuum. These moulds nevertheless have the inconvenience of a limited working life, owing to, for the one hand, mechanical deterioration by erosion of the joints of the mould, formation of leaks, or by breakage or chipping, and on the other hand, to a progressive blocking up of the pores in the material by salts from the barbotine and/or the plaster itself. The regeneration of a plaster mould by washing and drying is practically impossible due to the instability of plaster which is susceptible to dissolution in water and dehydration. One of the objects of the present invention is to provide a material which permits moulds to be obtained which have mechanical properties and permeability at least equal to those of the present moulds, but which are capable of being dried at higher temperatures, thus more quickly, and which can be regenerated by washing when they have been choked by the deposition of salts. Moreover, plaster is used for purposes other than in the ceramic industry, thanks to its porous nature which gives rise to valuable thermal insulation properties and also permeability to liquids and to gases, and thanks to the facility with which it permits satisfactory surface states to be obtained, but these uses are often limited by the defects mentioned above.
Another object of the invention is to provide a material which can be used in a manner analogous to plaster, for example in the form of coatings obtained by rendering, without having the same limitations, or which can be used as a filter or catalyst support.